176496: Can he say du ‘aa’ between the two prostrations in words other than those narrated from the Prophet (blessings and peace of Allah be upon him)?

Is it wajib or sunnah to say a dua in jalsa? Like saying "rabbighfirli" 3 times or any other dua.
I just recently found out about this and am confused on whether it is sunnah or wajib.
If it is wajib, will all my past salah count?

Praise be
to Allah.

It is better for the worshipper
to say du‘aa’ between the two prostrations in the words narrated from the
Prophet (blessings and peace of Allah be upon him), as it was narrated by an-Nasaa’i (1145) from Hudhayfah
(may Allah be pleased with him) that the Prophet (blessings and peace of Allah
be upon him) used to say between the two prostrations: “Rabb
ighfir li, Rabb ighfir li
(Lord forgive me, Lord forgive me).”

Classed as saheeh by al-Albaani in Saheeh Sunan an-Nasaa’i.

At-Tirmidhi
(262) narrated from Ibn ‘Abbaas
(may Allah be pleased with him) that the Prophet (blessings and peace of Allah
be upon him) used to say between the two prostrations: “Allahumma
aghfir li wa’rhamni wa’jburni wa’hdini wa’rzuqni (O Allah, forgive me, have mercy on me, console me, guide me and grant
me provision).”

Classed as saheeh by al-Albaani in Saheeh Sunan at-Tirmidhi.

With regard to adding to the du‘aa’ that was narrated from the Prophet (blessings and
peace of Allah be upon him) or using words other than those that were narrated,
what appears to be the case is that it is permissible, because this is a
posture (of the prayer) in which du‘aa’ is allowed.
However it is preferable – as stated above – to limit it to what was narrated
from the Prophet (blessings and peace of Allah be upon him), and to say du‘aa’ in words other than those which were narrated when
prostrating or before saying the salaam at the end of the prayer. Muslim (479)
narrated from Ibn ‘Abbaas
(may Allah be pleased with him) that the Prophet (blessings and peace of Allah
be upon him) said: “and as for prostrating, strive in du’aa’,
for it is deserving of a response (from your Lord).”

Shaykh Ibn Baaz (may Allah have mercy on
him) said: Then he should rise from prostration and say, “Rabb
ighfir li, Rabb ighfir li,
Rabb ighfir li (Lord forgive me, Lord forgive me, Lord forgive
me),” as the Messenger (blessings and peace of Allah be upon him) used to do.
And it is mustahabb to say along with that: “Allahumma aghfir li wa’rhamni wa’hdini
wa’jburni wa’rzuqni wa ‘aafini (O Allah, forgive me,
have mercy on me, guide me, console me, grant me provision and grant me well
being),” because it is proven that the Prophet (blessings and peace of Allah be
upon him) used to say that. And if he wants to add to that, there is nothing
wrong with it, such as saying: O Allah, forgive me and my parents; O Allah,
admit me to Paradise and save me from the Fire; O Allah, rectify my heart and
my deeds, and so on. But he should offer a lot of du‘aa’
for forgiveness between the two prostrations, as was narrated from the Prophet
(blessings and peace of Allah be upon him).

End quote from Majmoo‘
Fataawa ash-Shaykh
Ibn Baaz, 11/36

Shaykh Muhammad ibn Muhammad al-Mukhtaar ash-Shanqeeti (may Allah preserve him) said: The Prophet
(blessings and peace of Allah be upon him) used to ask for well-being between
the two prostrations, because this is the place of du‘aa’.
The scholars had two opinions concerning that. Some of them said: It is a place
for du‘aa’, so it is prescribed for a person to offer
whatever du‘aa’ he likes concerning his affairs in
this world and in the Hereafter. Others said: He should limit it to what has
been narrated (from the Prophet (blessings and peace of Allah be upon him)),
and this view is stronger. But if he has not memorised
it, such as if he is one of the ordinary people, there is nothing wrong with
him saying whatever du‘aa’ he can.

The reason why he may say
whatever du‘aa’ he can is that the Sunnah is two things: the first is saying du‘aa’ and the second is the specific wording. If he is not
able to say the specific wording, then the Sunnah is
to ask of Allah. This is the view of the majority, as more than one scholar
attributed it to them. So if he is not able to memorise
the wording that was narrated, or he does not know it, and he says whatever du‘aa’ he is able to, such as offering du‘aa’
for himself and his parents, there is nothing wrong with that. But it is
preferable and better to say the du‘aa’ that was
narrated from the Prophet (blessings and peace of Allah be upon him).